1. Field of the Invention
The present invention relates to a diaphragm type load detection sensor, a load detection unit, and an electronic scale using the same.
2. Prior Art
At first, a diaphragm type load detection sensor in the prior art is briefly described with reference to FIG. 21. In particular, FIG. 21A is a plan view of the diaphragm type load detection sensor in the prior art; FIG. 21B is a cross section view of the sensor, taken along a line D—D in FIG. 21A; and FIG. 21C is a cross section view of the sensor, taken along a line E—E in FIG. 21A. The diaphragm type load detention sensor in the prior art comprises a mounting portion 1, a strain generation portion 2, and a load applied portion 3 having a projection formed thereon, wherein a strain gauge 4 including a plurality of sensing elements is affixed to the strain generation portion 2. The strain gauge 4 has a lead wire 4A connected thereto. In this example, the strain gauge 4 is affixed in a line such that the sensing elements are positioned in bilateral symmetry about the center of the projection of the load applied portion 3. In another example, the strain gauge is affixed to the strain generation portion in such manner that the sensing elements are positioned in bilateral and vertical symmetry about the center of the projection of the load applied portion (refer to Patent Laid-Open No. 2000-346723, FIG. 1).
Referring to FIG. 22 which is a cross section view of another diaphragm type load detection sensor in the prior art, it comprises a mounting portion 1, a strain generation portion 2, and a load applied portion 3, wherein a strain gauge 4 including a plurality of sensing elements is affixed to the strain generation portion 2. The strain gauge 4 has a lead wire 4A connected thereto. The diaphragm type load detection sensor is configured in such manner that when a load is applied to the load applied portion 3 the strain generation portion 2 is deformed, and consequently, the plurality of sensing elements of the strain gauge 4 are deformed. Then, the deformation of the sensing elements (or resistance change) is electrically detected via the lead wire 4A to detect the load applied to the load applied portion. In this example, the strain gauge 4 is affixed in a line such that the sensing elements are positioned in bilateral symmetry about the center of the projection of the load applied portion 3. As shown in FIG. 22, for example, the diaphragm type load detention sensor in the prior art is secured to an installation plate 5 such as a base of a scale using a screw 6 (refer to Patent Laid-Open No. 2000-346723). Alternatively, as shown in FIG. 23, it is secured to the installation plate 5 by welding the mounting portion 1 thereto, as indicated by a reference numeral “7”.
However, in the diaphragm type load detention sensor in the prior art wherein the strain gauge is affixed in a line such that the sensing elements are positioned in bilateral symmetry about the center of the projection of the load applied portion, as described with reference to FIG. 21, if a load is obliquely applied to the load applied portion 3 (as indicated by an arrow “F”), as shown in FIG. 21C, then any difference in output may be produced due to such obliquely applied load “F”. The reason for which is that the strain gauge (or the sensing element) would receive different contribution depending on whether a horizontal component of the obliquely applied load “F” to the load applied portion (as indicated by an arrow “H”) is exerted in parallel with the gauge line, as shown in FIG. 21B, or in normal to the gauge line, as shown in FIG. 21C. This is also true for the diaphragm type load detention sensor, as disclosed in Patent Laid-Open No. 2000-346723. In particular, any difference in output may be produced depending on whether the load is obliquely applied to the direction of gauge line or the load is obliquely applied to the direction that is angled to the gauge line.
Furthermore, in the diaphragm type load detention sensor that is directly coupled to the installation plate 5 with screws, if a load is obliquely applied to the projection of the load applied portion 3 then the boundary between the mounting portion 1 and the installation plate 5 may be slightly shifted to change the restricting condition, thereby promoting occurrence of output difference depending on the direction of the obliquely applied load “F”.
In view of the above an object of the present invention is to provide a diaphragm type load detection sensor, a load detection unit and an electronic scale using the same, which can solve the prior art problems, as described above.